Photoelectric colorimeter



March l2, 1940a K. A. EVELYN PHOTOELECTRIC COLORIMETER 3 Sheets-Sheet lFiled March '7, 1938 Ilflllliilifliilllllllf. .ill llllilllllllliINVENTOR KENNETHAV-ELYN .1v-69.250 d@ ATTORNEY Illllllll March l2, 1940.m., vELYN PHOTOELEQ'RIC COLORIMETER 3 Sheets-Sheet 2 Filed March 7, 1938E F/V//////////////r///////// f//////////////// /r//A Irl YMardi l2,1940. K' A. EVELYN 2,193,315

PHOTOELECTRIC COLORIMETER Filed March 7, 1938 3 Sheets-Sheet 3 5655PEclAL 51205 585s GEOS ouocunowmc 0 /\/L/\ caMBmATloNs 40o 500 60o 400 544o 490 52o 54o 530 620 660A EIO STANDARD E commnmous n: o v E o 500600, 700m): E BLUEAND 5,1 GREEN E25 SERIES U 400 50o 60o mamy 50 REDANDw 25 SERIES 0 o WAVELENGTH m MlLuMxcRous "f INVEN TOR KENNETHAEVELYNhuma iz, i940 uNlraows'rATas PATENT ori-Ica 2.193.815 PBOTOELECTRICOOLORIMETER 'Kenneth A. Evelyn. Montreal, Qnebec, Canada ApplicationMarch 7, 1938, Serial No. 194,388 s calm.` (ci. ssio This inventionrelates to improvements in photoelectrlc colorimeters for use inbiological work and in other relations.

Photoelectric colorlmeters forbiological work fall into two mainclasses. The ilrst is the single photocell type in which a solution ofthe substance under test is placed between the cell and the source oflight. The second is the double photocell type in which the substanceunder test l0 is interposed between the source of light and one of twocells which are balanced against each other in a suitable electricalnetwork.

In the single cell instrument a beam of light falls on a photocell whichproduces a dedection W in a galvanometer to which it is connected. If anabsorption cell containing a colored solution is placed between thesource of light and the pho-f toelectric cell, the percentage of lighttransmitted through the solution is proportional to the ratio of theilnal to the initial galvanometer deiiection. The concentration of thecolored substance in the sample can then be read from a prepared chartshowing the variation of light transmission with concentration.Increased y accuracy Y may M be obtained by using color lterswhichtransmit only that portion of the spectrum in which the solutionhas the correct degree of absorption. It is essential to successful useof this instrument that the source of light be of absolutely constantintensity. Diinculties encountered in meeting this requirement have ledto the adoption of the double cell instrument. Inthe latter both cellsare equally affected by changes in the intensity of the light source sothat .these changes do not 88 ail'ect the galvanometer lor othermeasuring instrument through which the cells are balanced against eachother. In the use of the double cell instrument the light absorption oi'the solution under test is indicated by the extent to which the cellsare unbalanced when the test sample is interposed between the lightsource and one of the cells. The principal diiliculty with the doublecell instrument is the erratic behaviour which it exhibits as a resultof unavoidable asymmetry 4B of the response of the two cells to light ofdiierent wave lengths.

In orderto obtain the required high degree oi' precision with either thesingle or double cell photoelectrlc colorimeters now available it is 50usually necessary to interpose some form oi' adjustable lightcontrolling means, such as an adjustable diaphragm, between the lightsource and the sample under test in order to compensate for changes inthe intensity o! the light source or in as the current output of thecellor cells. The movvveniently interposed able parts thus introduced intothe instrument materially increase the possibility of errors due topurely mechanical causes and render the instrument less convenient tooperate.

The instrument provided in accordance with 5 the present inventioncomprises a simple and conveniently operated colorimeter in which theusual causes of unsatisfactory performances are eliminated by completemechanical rigidity, absence of moving parts, and a large safety factorl0 in all important components. In this instrument complete mechanicalrigidity is achieved by rigid attachment of the light source and cell toopposite sides of an absorption tube holder in line with suitableapertures through which the beam of l5 light passes from the lightsource to the cell. The light source comprises a lamp mounted in ahemispherical reiiector rigidly secured to the tube holder. The lampused is of exceptionally low power requirement and is run so far belowits go rated voltage that its useful life is equivalent to almost oneyear of hard service. In practice satisfactory results have beenobtained by using a Mazda No. 31 ashflight bulb mounted in ahemispherical matte-surfaced aluminum reiiector. 25 This simplearrangement has many important advantages. The power requirement (1watt) and the current drain (200 milliamperes) are so low that the lampcan be energized by a 6-volt storage battery or by a standard 6-voltvoltage so regulating transformer. This ensures extreme stabilityoflight intensity over long periods of time. The small current in thelamp also simplies the problemof controlling the light intensity, sinceheating eil'ects in rheostats employed 35 in the control circuit are ata minimum. Ihe light intensity can be varied smoothly over a wide range(200 fold) by the use of a comparatively simple control circuit. Thesmooth control of light intensity over a wide range and the 40 highilluminating eftlciency obtained by the use of the reector permit use ofcolor filters of very high selectivity and thus greatly extend the scopeof the apparatus. The color lters are conbetween the light source andthe absorption tube by means of a lter holder or slide inserted in asuitable compartment of the tube holder.

The extreme stability of light intensity which is characteristic of thelight source provided in accordance with the present invention rendersunnecessary the use of a diaphragm or other ad- ,instable lightcontrolling means between the light source and the absorption tubes.

This invention also contemplates the provision gg of two sets ofcarefully chosen filter units from which various combinations may beselected to isolate bands'with transmission maxima at intervals ofapproximately 20 millimicrns throughout the visible spectrum. Each ofthese composite filters or lter combinations may consist of 2, 3, ormore properly selected units mounted in a common holder and has theadvantages of being stable and reproducible.

Proceeding now to a more detailed description reference will be had tothe accompanying drawings, in which- Figure 1 is a schematic view of theessential components of Awhat is now considered to be the preferredembodiment of the invention.

Figure 2 is a view showing the tube holder in front elevation with thelamp and reflector removed. In this view the color filter holder and theabsorption tube are shown in the positions which they occupy when theinstrument is in use.

Figure 3 is a vertical sectional view of the assembly appearing inFigure 2, the plane of the section being substantially along the line 33 of Figure 2. In this view the reector and lamp are shown in place onthe tube holder.

Figure 4 is a complete plan view of the assembly appearing in Figure 3.

Figure 5 is a side elevation of a tubular liner` which is tted in theabsorption tube holder to take the absorption tube.

Figure 6 is a transverse section substantially along the line 6--6 ofFigure 5. I

Figure 7 is a curve diagram showing the spectrophotometric curves of anumber of composite filters and filter discs which are used inaccordance with this invention.

The general principles of the invention will vnow be described withreference to Fig. 1. A

beam of light from the lamp 5 in reector 6 passes through the color lter'l and then through the colored solution 8 contained in the absorptiontube 9. The absorption tube is mounted in the tube holder IIJ betweenthe rectangular apertures II and I2 which serve to define the crossVsection of the light beam. The transmitted light falls on the photocellI3, the current from which is indicated on the galvanometer I.

The lamp 5 is preferably a Mazda No. 31, 6.2 volt, flash-light bulbenergized by the 6volt power supply I5 of the simple control circuit I6.The manual controls in this circuit are the main lamp switch I'I, thelow range lamp switch I8 and the two rheostats I9 and 20. Smooth controlof the intensity of the light beam over a wide range is obtained byappropriate adjustment of the rheostats I3 and 20 which provide fine andcoarse adjustments, respectively. The rheostats I9 and 20 are connectedin parallel with each other but in series with a fixed resister 2| whichlimits the maximum voltage on the lamp to 5 volts, thus allowing anample safety factor over the normal operating voltage of the'lamp. Therheostat 20 is also connected -in series with a xed resistor 22. Theremaining resistor, indicated at 23, is the low range resistor which iscut into or out of the circuit at will by .appropriate operation 'ofswitch I8. The resistor 2l is not absolutely essential and may beomitted.

In practice I have found that the best results and maximum stability arerealized when a 6- volt lead storage battery is 'used asfa power supplyfor the lamp 5. If this high degree of stability is not required astandard 6volt voltage regulating transformer may be substituted. Whereportability is desired, satisfactory performance can be obtained with a6volt dry battery.

The photoelectric cell I3 is connected directly to the galvanometer I4,for which it supplies a suitable external damping resistance. Sinceheating effects are reduced to a minimum by the small current used inthe lamp circuit and since the photocell is exposed to very lowintensities of illumination (less than 1-foot candle power) it followsthat, in the instrument provided in accordance with the presentinvention, photoelectric fatigue and temperature effects are negligible.In this connection it may be pointed out that a great deal of theinstability of certain photoelectric devices, commonly attributed tophotoelectric fatigue," is really due to heating effects in overloadedlamp circuits.

The galvanometer Ill should have a period of three seconds or less, acoil resistance of about 1000 ohms, and an external critical dampingresistance of about 5000 ohms. A full scale deflection of divisionsshould correspond to a current of about 2.5 microamperes.

The absorption tube S is preferably a standard, round bottomed, softglass test tube. I have found that the substitution of this type of tubefor the conventional rectangular glass cell greatly simplifies theoperation and construction of the colorimeter. Since manyinterchangeable tubes are available one may carry out the entireproceeding (except in a few special cases) in the same tube in which thefinal colorimetric reading is to be made. As the act of making a readingdoes not in any way interfere with the solution underA test serialreadings on large numbers of samples may be made as often as desired.This is particularly important in the case of volatile media. Theability to make rapid serial readings on numerous samples is invaluablein the study of the effect on colorimeter reactions of time,temperature, pH, and other variables. Another characteristic feature dueto the use of a standard test tube as the absorption cell is that, whena blank tube filled with a colorless solvent is placed in the holder, itacts as a cylindrical lens which concentrates the light beam on thephotocell. The galvanometer reading with a blank tube is thereforegreater than the corresponding reading with the holder empty. The ratiobetween the two is about 1.5 and is determined by the geometry of thesystem, the wave length of the light, and the refractive indexof thecontents of the tube. Since this ratio is constant for any one type ofdetermination it is immaterial whether the initial deection is adjustedwith the holder empty or with a blank tube (containing solvent only) inplace.

The operation of the instrument described herein may be briefly setforth as follows: The proper color lterl 1 is selected and interposedbetween the lamp 5 and the tube 9. A blank tube, containing puresolvent, is inserted in the holder I0 and the rheostats I9 and 20adjusted until an initial deflection of 100 divisions is obtained. Theblank tube is now replaced by the sample tube, the new deflection isnoted and the corresponding value of the concentration is obtained fromthe proper calibration chart.

The preferred mechanical assembly of the absoption tubeholder andassociated parts to 70 Bakelite sleeve 28 is removably fitted in thebore 25. 'Ihe lower end of this sleeve is closed by a plug 29 whichsupports the rounded bottom of the test tube 9. Apertures 30, 3|, 32 and33 are formed in the lower portion of the sleeve ,28. The apertures 39and 3| are located directlyopposite each other and are both of exactlythe same size as the apertures Il and I2 of the holder I9. The apertures32 and 33, which are also opposed to each other, are located between theapertures 30 and 3| and are somewhat smaller. With the sleeve 28 in theposition shown in Fig. 3, the sleeve apertures 39 and 3| arerespectively aligned with the apertures Il and I2 of the holder. Incases where the level of the solution contained in the inserted tube 9is below the upper edges of the apertures II and I2 (see dotted line 8ain Fig. 1) the sleeve 28 is rotated through a suitable angle to positionthe small apertures 32 and 33 in line with the apertures II and l2. Thesleeve 28 is held against accidental turning movement inthe holder I bymeans of the steel ball `34 and the spring 35 shown in Fig. 3. The ball34 works in an opening in the holder I 8 and is pressed inwardly by thespring 35 to engage in either of the circumferentially spaced recesses36 and 31 provided in the wall of the sleeve 28. 'Ihese recesses arearranged so that the ball 34 engages in the recess 36 when the sleeveapertures 38 and 3| are aligned with the apertures II and I2 and withthe recess 31 when the sleeve apertures 32 and 33 are substituted forthe apertures 30 and 3|,

A plate 38 is soldered or otherwise secured -to the flattened side 21 ofthe holder i8. This plate is provided with a rectangular aperture 39matching the .aperture I2 of the holder. The photoelectric cell I3iscentered over the aperture 39 and is clamped against the outer surfaceof plate 38 by a hard rubber strap 40. Strap 48 is fastened to plate 38by studs 4| and thumb nuts 42 and is provided with suitable apertures 43for the passage of the cell terminals 44.

A color filter slideway or compartment, generally indicated at 46, isrigidly attached to the side of the holder I0 opposite the photocell I3.The front and rear walls of this slideway or compartment are formed bymetal plates 48 and 49, the latter being soldered or otherwise rigidlyfastened to the attened side 26 of the holder I0. The side walls of thefilter slideway or compartment are formed by strips 58 which are securedbetween the longitudinal edges of the plates 48 and 49 by suitablescrews or other fastening means.

The rear plate 49 of the filter compartment is provided with arectangular aperture matching the aperture II of the holder I8. 'I'hefront plate 48 of the iilter compartment is provided with a relativelylarge circular aperture 52 surrounded by an outwardly projecting flange53. 'Ihe open side of the reflector 8 is tted within the ange 53 to bearagainst the outer surface of the plate 48 as shown to advantage in Fig.3, The reflector is secured in this position by a clamping strap 54which bears against the stem of the lamp 5. The ends of the strap 54 arefastened to the filter compartment by means of the posts 55 and thethumb nuts 56.

Single or composite color iilters used in accordance with the presentinvention may be conveniently interposed between the light source andthe absorption .tube through the agency of a lter slide adapted to beinserted in the filter compartment 46. This slide comprises a plate 81provided with openings 58 and 59 for the reception of two filtersindicated at 1. Each opening is bounded, at one side, by an inwardlyprojecting ledge 8| against which the filter is clamped by a splitretaining spring 82. 'I'he plate 51 of the iilter slide is movedvertically in the lter compartment by means of the handle rod 83 and isprovided with notches 94 and 65 adapted to be selectively engaged by adetent generally indicated at 68. Two filters are mounted in the illterslide so that a change fromy one type of filter to another may Ibeconveniently made by moving the filter slide up or down in the filtercompartment. In using the lower filter the filter slide is moved up tothe proper position in which it is secured by engagement of the detent68 in the notch 55. When the filter slide is moved down to interpose theupper filter between the light source and the absorption tube, it isheld against accidental displacement by engagement of the detent 56inthe upper notch 64. As here shown the detent 68 comprises a ball 89which is forced inwardly through an opening in one side of the filtercompartment by a cylindrical member 'I0 fixed to the upper end of aspring 1 I.

In the present instance the plug 29 of sleeve 28 is provided with a hardrubber centre 29a whose upper end is surrounded by a soft rubber washer29h. Therounded bottom of the test tube 9 is supported by the portions29a and 29h of the plug as shown to advantage in Fig. 3.

Single or composite filters used with the col` orimeter described hereinare selected from two sets of unit filters (see Fig. 7) which removeprogressively longer and shorter wave lengths respectively so that anydesired band may be isolated by selecting a single unit having therequired transmission characteristics or by combining appropriate unitsfrom each set. The two upper sets of curves shown in Fig. 7 arerepresentative of a few of the composite filters provided in accordancewith this invention, while the two lower sets of curves arerepresentative of the characteristics of a number of the componentfilter discs from which the composite ltersare formed. The transmissioncurves of the unit iilters-of the two sets should be such that selectedunits from each set may be combined to provide a series of narrowtransmission iilter combinations capable of isolating bands withtransmission maxima at intervals of approximately 20 millimicronsthroughout the visible spectrum. As an illustration of the flexibilityof the filter stock, five examples of spectrum transmission filtersprovided in accordance with this invention are represented in Fig. 7.

To ensure uniformity of filter unitsmf the same type, i. e., duplicateunits of eitliejnset, they are preferably made from a `single 'ltf ofglass from which samples have been ground for spectrophotometricstandardization. Since slight variations in color density in diffe entparts of the same melt are unavoidable each unit should be checkedagainst a suitable standard to which it must conform.

Having thus described my invention, what I claim is:

1. A photoelectric colorimeter comprising rigidly united cell andfilter-slide holders each having, in opposite portions of its wallstructure, openings arranged to register with each other and with theopenings of the companion holder, a photoelectric cell rigidly securedto the cell holder over the opening therein which is furthest from thelter-slide holder, a reiiector rigidly secured to the filter-slideholder over the opening therein which is furthest from the cell holder,an electric light bulb mounted in said reflector in line.,-'with saidopenings, said cell holder being provided between the openings thereinwith a. ,cylindrical cell receiving bore, a cylindrical lining sleeverotatably mounted in said bore and provided with two pairsipi open-`ings formed in the circumferential wall thereof,

said sleeve openings being arranged so that the openings of each pairlie diametrically opposite each other and may bebrought opposite theopenings in the cell holder by appropriate rotation of the sleeve, theupper edges of one pair of sleeve openings lying in a common horizontalplane located between horizontal planes containing the upper and loweredges of the openings in the cell holder and below a horizontal planecontaining the upper edges of the companion pair of sleeve openings; anda'cushioning plug closing the lower end of said sleeve and serving as acushioning support for va cell placed therein.

2. A photoelectric colorimeter as set forth in claim l including meansfdr holding the'lining sleeve in different positions of adjustment towhich it is rotated to bring selected openings of the sleeve in registrywith the openings of the cell holder.

3. In a photoelectric colorimeter, a cell holder provided with acylindrical bore intersecting openings formed in opposite side walls ofthe holder, a cylindrical lining sleeve rotatably mounted in said boreand provided with two pairs of openings formed in the circumferentialwall thereof, said sleeve openings being arranged so that the openingsof each pair 'lie diametrically Opposite eachother and may be broughtopposite the openings in the cell holder by appropriate rotation of thesleeve, the upper edges oi7 one pair of sleeve openings lying in acommon horizontal plane located between horizontal planes containing theupper and lower edges of the cell holder openings and below a horizontalplane containing the upper edges of the companion pair of sleeveopenings.

4. A photoelectric colorimeter comprising a cell holder provided with acylindrical bore intersecting openings in opposite side walls of theholder, a filter-slide holder having openings formed in opposite sidewalls thereof and having one of said side walls rigidly secured to oneof the aforesaid side walls of the cell holder so that the openings inthe two holders are disposed in alignment, a photoelectric cell rigidlysecured to the cell holder over the opening therein which is furthestfrom the iilter-slide'holder, a reii tor rigidly secured to thelter-slide holder ovethe opening therein which is furthest from the cellholder, an electric lightbulb mounted in said reector in line with saidopenings, and a cylindrical lining sleeve rotatably mounted in thecylindrical bore o1' the cell holder and provided with two pairs ofopenings formed in the circumferential wall thereof, said openings beingarranged so that the openings of each pair lie diametrically oppositeeach other and may be brought opposite the openings in the cell holderby appropriate rotation of the sleeve, the upper edges of one pair ofsleeve openings lying in a common horizontal plane located betweenhorizontal planes containing the upper and lower edges of the openingsin the cell holder` and below a horizontal plane containing the upperedges of the companion pair of sleeve openings.

5. A photoelectric colorimeter as set forth in claim 4 including alter-slide mounted in the lter-slide holder and provided with upperandlower filters adapted to be selectively aligned with the openings insaid illter-slide holder by sliding movement ofthe filter-slide relativeto the filter-slide holder, said filter-slide and lterslide holder beingprovided with cooperating means for retaining'the lter-slide againstaccidental movement when either of the lters is aligned with theopenings in the filter-slide holder.

6. In a photoelectric colorimeter, a cell holder provided with a boreintersecting openings formed in opposite walls of the holder, acylindrical lining sleeve rotatably mounted in said bore and providedwith two pairs of openings formed in the circumferential wall thereof,said sleeve openings being arranged so that the openings of each pairlie diametrically opposite each other and may be brought opposite theopenings in the cell holder by appropriate rotation of the sleeve, theupperv and lower edges of one pair of sleeve openings being co-planarwith the upper and lower edges of the openings in the cell holder, theremaining pair of sleeve openings having their lower edges-co-planarwith the lower edges of the openings in the cell holder but their upperedges located in a lower plane relative to the plane containing theupper edges of the cell holder openings.

A. EVELYN.

